Conservation of energy is a critical national and worldwide concern. Continuous lighting in empty rooms is an unnecessary waste of energy. Some state and local energy conservation/building codes require installation of two light switches in the construction or reconstruction of offices, each to control a different portion of the overhead lighting. The reasoning behind such requirements is that in the interest of energy conservation, employees and janitorial personnel may be offered the opportunity to use approximately one half of the light they would normally require in their day-to-day activities. Depending upon the amount of ambient light available, employees working in a room may select to use only one half of the available bank or banks of lights.
Further, employees may tailor their specific lighting needs to their activities and location in the room. For example, employees working in an area not receiving sufficient ambient light may require more artificial light, depending upon their specific activities. Similarly, employees located in an area receiving sufficient ambient light may require less artificial light. Utilizing office lighting effectively, such that only approximately fifty percent is sometimes used and only in occupied offices, results in substantial energy savings. In addition, for computer applications, it is advantageous to reduce the level of light to eliminate the glare on cathode ray tubes (CRT). Conventional manual switches are inefficient because they depend upon human judgment to turn all or only a portion of the lights on and off. Existing automatic wall switches have also proven to be inefficient. For example, currently available light switches or the like used in offices emit an ultrasonic wave into a room and detect motion of persons by sensing a doppler-shift in the reflected ultrasonic wave. The doppler-shift in the reflected wave is caused by persons moving within the room.
Typically, these ultrasonic light switches are preset to a sensitivity level such that a person moving anywhere within the room is detected. Because the preset sensitivity level for the reflected ultrasonic wave is fixed, a wall switch located adjacent an open door can detect persons moving outside the door and unnecessarily turn on the lights within the room.
Although a wall switch that turns lights on automatically is preferable in most instances, in some applications occupants prefer a manual option for activating lights. For example, in situations where a person enters the room for a very brief period of time, such as a secretary delivering papers, the lights do not need to be turned on. Another example is a situation in which there is adequate ambient light.